Soymilk, for example, is produced from a go-eki having soybeans ground together with water. In producing the soymilk, a hopper (raw material supply apparatus) for supplying the soybeans and water is used. As the conventional hopper (raw material supply apparatus) of this type, the hopper disclosed in patent document 1 as JP H07-144140 A or patent document 2 as JP 2005-304474 A, for example, has been used.
On the other hand, the applicant of the present application has already proposed an apparatus for crushing and grinding solid raw materials including cereals or medicinal raw materials with a submerged grinding apparatus as disclosed in patent documents 3 as JP 2006-15206 A and patent documents 4 as JP 2007-69206 A, in which a hopper (raw material supply apparatus) is exemplified (in FIGS. 15 to 18 of patent document 3, for example).